How do I get a count of associated rows in a left join in MySQL?
Question
I have two tables, a vehicle
table with columns:
id
stock
year
make
model
and an images
table with columns:
id
vehicle_id
name
caption
default tinyint(1)
I am trying to list the vehicle's information, its default image, and a total count of images the vehicle has. Currently I am using the following SELECT
statement:
SELECT vehicle.id, vehicle.stock, vehicle.year,
vehicle.make, vehicle.model, images.name,
COUNT(images.id)
FROM vehicle
LEFT JOIN images
ON vehicle.id = images.vehicle_id
I initially was using:
ON vehicle.id = images.vehicle_id AND images.default = 1
but then the images count would only be 1 or 0 depending if there was a default image in the database. I have tried using UNION
and other SELECT
statements but I am still unable to get a proper result. Do I need to use two SELECT
statements or is there another way to handle it with JOIN
or UNION
?
Solution
SELECT
`vehicle`.`id`,
`vehicle`.`stock`,
`vehicle`.`year`,
`vehicle`.`make`,
`vehicle`.`model`,
`images`.`name`,
(
SELECT COUNT(*)
FROM `images`
WHERE `vehicle_id` = `vehicle`.`id`
) AS `image_count`
FROM `vehicle`
LEFT JOIN `images`
ON `images`.`vehicle_id` = `vehicle`.`id`
WHERE `images`.`default`
OTHER TIPS
In the way the anser suggests, you get repeated values of "vehicle". A better way, is to group results. Try without the JOIN :
SELECT
`vehicle`.`id`,
`vehicle`.`stock`,
`vehicle`.`year`,
`vehicle`.`make`,
`vehicle`.`model`,
`images`.`name`,
(
SELECT COUNT(*)
FROM `images`
WHERE `vehicle_id` = `vehicle`.`id`
) AS `image_count`
FROM `vehicle`
WHERE `images`.`default`
Let me make it clear for everyone!
Task: Print 3 columns table:
- Vehicles (titles) from vehicles table.
- Amount of comments for each vehicle from comments table.
- Amount of images for each vehicle from images table.
Expected output (just an example):
+----------------------+----------------+--------------+
| title | comments_count | images_count |
+----------------------+----------------+--------------+
| BMW X6 | 35 | 9 |
| Audi A6 | 3 | 5 |
| Volkswagen Passat B6 | 78 | 6 |
| Volkswagen Passat B5 | 129 | 4 |
+----------------------+----------------+--------------+
Solution:
SELECT
vehicles.title,
(SELECT COUNT(*) FROM comments WHERE vehicles.id = comments.vehicle_id) AS comments_count,
(SELECT COUNT(*) FROM images WHERE vehicles.id = images.vehicle_id) AS images_count
FROM vehicles